Equine infectious anemia is a persistent viral infection with a number of immunologically mediated lesions. Infected horses have circulating antibodies measurable by several techniques, yet the blood is still infectious for horses. The research proposed here will be directed toward evaluation of the humoral and cellular immune processes and their interaction with the virus. The pathogenesis of the lesions will be investigated in detail. The virus and associated antigens will be characterized. The data obtained will be evaluated to delineate the mechanisms of viral persistence and of the pathogenesis of the lesions.